convert streamed buffers to utf8-string

Question

I want to make a HTTP-request using node.js to load some text from a webserver. Since the response can contain much text (some Megabytes) I want to process each text chunk s

Answer 1

var fs = require("fs");

function readFileLineByLine(filename, processline) {
    var stream = fs.createReadStream(filename);
    var s = "";
    stream.on("data", function(data) {
        s += data.toString('utf8');
        var lines = s.split("\n");
        for (var i = 0; i < lines.length - 1; i++)
            processline(lines[i]);
        s = lines[lines.length - 1];
    });

    stream.on("end",function() {
        var lines = s.split("\n");
        for (var i = 0; i < lines.length; i++)
            processline(lines[i]);
    });
}

var linenumber = 0;
readFileLineByLine(filename, function(line) {
    console.log(++linenumber + " -- " + line);
});

Answer 2

Single Buffer

If you have a single Buffer you can use its toString method that will convert all or part of the binary contents to a string using a specific encoding. It defaults to utf8 if you don't provide a parameter, but I've explicitly set the encoding in this example.

var req = http.request(reqOptions, function(res) {
    ...

    res.on('data', function(chunk) {
        var textChunk = chunk.toString('utf8');
        // process utf8 text chunk
    });
});

Streamed Buffers

If you have streamed buffers like in the question above where the first byte of a multi-byte UTF8-character may be contained in the first Buffer (chunk) and the second byte in the second Buffer then you should use a StringDecoder. :

var StringDecoder = require('string_decoder').StringDecoder;

var req = http.request(reqOptions, function(res) {
    ...
    var decoder = new StringDecoder('utf8');

    res.on('data', function(chunk) {
        var textChunk = decoder.write(chunk);
        // process utf8 text chunk
    });
});

This way bytes of incomplete characters are buffered by the StringDecoder until all required bytes were written to the decoder.